Pop star John (5)
I believe the answer is:
elton
'pop star john' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for elton that I've seen before include "- John, British singer" , "Let on he's John, the singer" , ". . . . . John (musician)" , "Ben --; -- John" , "Sir ___ John, singer-songwriter" .)